ISSUE-13: Remove 'background-origin'

background-origin

Remove 'background-origin'

There are some problems and sources of confusion associated with 'background-origin':

1) The 'background-origin' influences the 'background-position' so that in a style sheet you would normally specify them together, which in turn suggests that they should be merged. Or that 'background-origin' should be dropped, maybe in favor of a keyword in 'background-position': '10px from-border-edge'.

2) The 'background-origin' also influences the 'background-size', suggesting that *they* be merged.

3) The 'background-origin' and the 'background-clip' are likely to be very often the same (although by default, and in level 2, they are not). Elika suggested a keyword for 'background-clip' that means "same as 'background-origin'" so that you can specify globally that all clips should be the same as the origins.